The present invention relates to an image forming method and an image forming apparatus, such as a printer, facsimile, or copying machine or the like.
A known form of a photocopier produces a printed image on a piece of paper by forming an electrical image on a photoconductive member, applying toner to the electrical image, and transferring the toner to a paper sheet to form an image thereon, which is then fixed. Such a photocopier-must be provided with a photoconductive member, a charger, an exposure device, a developing device, a transfer device, a static eliminator, a cleaning device, a fixing device and the like. Thus, it is difficult to produce a photocopier that is compact and relatively cheap.
Furthermore, such a photocopier forms a toner image on the paper and then fixes the toner image using a fixing device. Therefore, if an unnecessary portion of the toner adheres to the paper in processes preceding the fixing process, the unnecessary portion of the toner is fixed together with the toner image, causing a blooming that deteriorates the picture quality.
An image forming apparatus disclosed in Japanese Patent Application JP-A-4-10955 controls the movement of particles of a toner with a light beam. The toner is constrained to move within a toner chamber and the light beam is directed at particles of the toner in order to move those particles onto a piece of paper. The toner on the paper is then subsequently fixed.
In this system, control of the motion of the toner particles is achieved by giving kinetic energy to the particles with a concentrated laser beam as they are floating in the air in the toner chamber. However, the movement of toner is very small because the duration of irradiation of the toner with the scanning light beam is comparatively short and the force produced by the light beam is comparatively low.
Since the motion of toner particles in the air must be controlled, and the motion of the particles is subject to the resistance of the air, any moving toner particles are brought to a stop in a relatively short time. In other words, it is difficult for the light beam to move the toner particles very far. Therefore when this image forming apparatus performs a scanning operation at a practical image forming speed, the distance of movement of the toner is in the order of 1 .mu.m. Therefore, each particle of the toner would have to be irradiated with light for a comparatively long period of time in order for the energy supplied to be sufficient to move each particle of the toner a sufficiently long distance to the paper. Hence, the image forming apparatus cannot complete an image in a practical amount of time.
Furthermore, if the particles of toner are irradiated with light for a comparatively long period of time, the motion of the irradiated particles of the toner are disturbed by the normal Brownian motions of the other toner particles, together with the variation of ambient conditions and, consequently, the formation of a clear image is prevented.
A further problem is that, since the distance of movement of the toner caused by the light is comparatively short, the size of the toner chamber must be relatively small when the toner is supplied in a floating state. However, it is difficult to supply the toner in a floating state through a thin space, as the toner circulating path in the chamber becomes clogged with the toner. It is therefore difficult to supply the image forming medium stably and consistently.
Furthermore, as the toner particles float within a circulating passage having an opening through which the toner particles are delivered to the paper, toner particles may "fall" through the opening onto the paper without being contacted by the light beam. This causes blooming.
An image forming apparatus disclosed in Japanese Patent Application JP-A-59-102269 irradiates a toner adhering to a toner conveying member with a laser beam in a developing and transferring unit in order to melt the toner, and to transfer and fix the toner to a recording sheet.
A paper entitled "Characteristics of Thermal Transfer Printing by Laser Heating (iii)--Study of Colour Printing Process" by Mitsuru Irie et al, from (pages 8-13), discusses thermal transfer colour printing using laser heating. In this process a coloured ink ribbon is placed against a piece of paper and ink is transferred from the ribbon to the paper using a laser beam.
In a paper entitled "Tonerjet--a Direct Printing Process" by Jerome Johnson et al, from (pages 509-512), a direct printing process is disclosed. In this process, charged toner particles are deposited directly onto a paper surface to form a visible image pattern. An array of wire mesh electrodes is used to create individual dot-sized electrostatic fields and charged toner particles are drawn through the wire mesh openings from a toner container and are deposited onto a plain paper surface in the desired visible image pattern. Once on the paper the toner particles are fused to form a permanent image.